1. Field of the Invention
The invention relates to an integrated structure of a micro-electromechanical system (MEMS) device and a complementary metal-oxide semiconductor (CMOS) image sensor (CIS) device and a fabricating method thereof, and more particularly, to an integrated structure of MEMS microphone and CIS device and a fabricating method thereof.
2. Description of the Prior Art
MEMS devices are tiny 3D-structures, such as circuits, micro-sensors, and micro-actuators, formed on wafers by microminiaturization technology. Such devices are operated based on electromagnetic, electrostructive, thermoelectric, or piezoresitive effect, exemplarily. Conventionally MEMS devices are formed on insulators or other substrates by micro-electronic techniques such as photolithograpy, vapor deposition, and etching. Nevertheless, it is a trend to fabricate MEMS devices by processes that have been applied in fabrication of conventional analog and digital complementary metal oxide semiconductor (CMOS) circuits.
Please refer to FIG. 1, which is a cross-sectional view of a conventional MEMS microphone. As shown in FIG. 1, a MEMS microphone 100 includes a silicon substrate 102 having a plurality of dielectric layers 104a, 104b, 104c, 104d, by which a plurality of metal layers 106a, 106b, 106c are respectively sandwiched therebetween, stacked and formed thereon. A portion of the metal layer 106a is patterned to form a micro-machined mesh metal 110; and other metal layers 106b, 106c are patterned to form openings above the micro-machined mesh metal 110 for exposing the micro-machined mesh metal 110.
The micro-machined mesh metal 110 of MEMS microphone 100 functions as a movable plate of a variable capacitor; it can be vibrated by a soundwave or contrarily pushes air to create a soundwave. Therefore vent holes are needed to connect the chamber 112, in which the micro-machined mesh metal 110 of the MEMS microphone 100 is positioned, to the external environment. If the chamber 112 and the micro-machined mesh metal 110 formed a vacuum, the micro-machined mesh metal 110 is not able to be pushed by soundwaves or push air to create the soundwaves. In the prior art, said vent holes 132 are formed by bonding a front surface of the substrate 102 to a carrier wafer 120 through a adhesive material 122, and followed by defining and etching a back side of the substrate 102 though a patterned hard mask 130. Thus the vent holes are obtained as shown in FIG. 1.
Please refer to FIG. 2, which is a cross-sectional view of a conventional CIS. The CIS 200 includes a silicon substrate 202 having a plurality of photodiodes 210 and a plurality of shallow trench isolations (STIs) 212 that provide electrical isolation between each photodiodes 210 formed therein. The CIS 200 also includes a plurality of dielectric layers 204a, 204b, 204c, by which a plurality of metal layers 206a, 206b are respectively sandwiched therebetween, formed on the silicon substrate 202. Said dielectric layers and the metal layers construct the multilevel interconnects as shown in FIG. 2.
Please refer to FIG. 2 again. The CIS 200 also includes a passivation layer 208 which protects above-mentioned elements from water, and a color filter array (CFA) 220 respectively corresponding to the photodiodes 210 formed on the front side of the silicon substrate 202. Furthermore, a planarization layer 222 and microlens 230 are formed on the CFA 220, and another protection layer 232 is formed on the microlens 230 to render protection to the microlens 230.
As mentioned above, it is a trend to fabricate MEMS devices by processes that have been applied in fabrication of conventional CMOS circuits. It is also a trend to integrate MEMS device and other devices in a wafer. However, when integrating the MEMS microphone and the CIS device, a problem emerges: The CFA of the CIS device is formed on the front side of the silicon substrate while fabrication of the vent holes of the MEMS microphone is performed on the back side of the silicon substrate. Therefore the CFA and the microlens on the front side of the silicon substrate are unavoidably damaged during fabricating the vent holes. Such problem makes the integration of MEMS microphone and CIS device not allowed.